This relates in general to devices for accurately measuring and checking angles, more particularly to sine bars and their methods of application to the machining of metal parts.
A sine bar is a device for measuring angles to a high degree of accuracy, which comprises one or more bars accommodating a pivot pin at one end and a bearing pin at the other end. The flat surfaces of the bar are ground to a high degree of accuracy, the distance between the tangential bearing points of the pivot pin and the bearing pin being accurately spaced-apart to form a hypotenuse (h) of preselected length when the bar is supported on a flat surface, or has a flat supporting bar, from which the reference bar is rotated about the pivot pin to form an angle. Precisely dimensioned gauge blocks are interposed beneath the bearing point at the open end, permitting accurate measurement of the subtended angle by the conventional formula sine O=a/h, where "a" is the height of the interposed gauge block and "h" is the length of the hypotenuse.
This principal is the basis of a prior art sine bar in wide use, comprising a single reference bar for use in conjunction with a flat base, and also, of an improved device entitled "Sine Bar For Lathe Attachment" disclosed in Russian Inventor's Certificate No. 278,353 granted to Kilin G.I. Glukhov on May 8, 1970.
The single element sine bar commonly used in the prior art cylindrical grinders, and other spindle-type machines to set a compound or a headstock accurately to a desired angle.
The problem with the improved model of the type disclosed in the Russian Inventor's Certificate to Glukhov is that the cylindrical body portion of the base member is strictly limited to cylindrical applications and cannot be used on flat surfaces, such as in milling, surface grinding, granite surface plates, and other similar applications. Moreover, it can only be mounted on spindle-type machines by using axially aligned centers at opposite ends of the bar, which limits the device to specific orientations, and thus, to specific applications. Glukhov's device is not designed to be mounted on a lathe by means of a collet or chuck at either end of the body, which limits its versatility, as it must always be mounted between centers.
Moreover, the Glukhov device and other prior art sine bars are not applicable to the measurement of very small angles, inasmuch as the height of the smallest gauge block which can be used is limited.
Furthermore, in the Glukhov device the gauge blocks are secured in place by tightening a nut at the pivot end, which distorts the measurement being made by changing the pressure within the reference sine bar.
Accordingly, it is the object of this invention to improve the accuracy of sine bar measurement by making certain improvements in the sine bar apparatus and the method of using the same.
More particular objects of the invention are to improve the accuracy of sine bar measurements, and the facility with which the sine bar can be used to perform many different types of measurements during lathe operations and other types of machining operations, as well as on milling machine tables, or other types of flat surfaces.
These and other objects are realized with the compound sine bar of my improved design and the disclosed methods of using the same. This comprises a flat reference bar having bearing means at opposite ends to accommodate a pivot pin at one end and a bearing pin at the other end. I have added a base member of substantially rectangular section hinged to the reference bar about the pivot pin, which permits the sine bar to rest on a flat surface. In addition, I have added to the two ends of the base member a pair of tailstock shaft extensions centered and protruding outwardly from opposite ends of the long axis of the base member which permit the base member to be mounted accurately into the collet of a conventional type of lathe, from either or both ends, or alternatively, to be mounted between centers. Since using the centered mounting members is optional, the operator is able to mount my improved sine bar in fixtures on milling machines, surface grinders and other equipment types having flat surfaces, where centers are not available and not practical.
Further, the base member of the sine bar of my design is provided with a recess on its upper surface which is based 0.100 inch below the horizontal plane of the tangential contact of the pivot pin, thereby enabling the use of supplemental blocks for the measurement of angles which are too small to be measured with prior art types of sine bars.
In accordance with another improvement, I employ a simple spring-biased chain arrangement fastened across the open angle between the reference bar and the base for holding the gauge blocks in place, thereby removing the necessity for tightening a nut at the pivot point, and thereby assuring the accuracy of sine bar angular setting.
In accordance with my improved method of using my sine bar to set up angles on a lathe compound, my sine bar is adjusted to the desired angle by interposing one or more gauge blocks, which are locked in place by the tension of the spring and chain. The tailstock shaft connection of my compound sine bar is then interposed into the collet of a lathe, where it is rotated to a desired position with its lateral surfaces in a horizontal position, as tested by a parallel flatstock bar placed across them. An indicator gauge is moved across the parallel flat stock bar to make sure the reference surface of the sine bar is parallel with the surface of the compound slide bar of the lathe compound. The lathe compound is then turned in a horizontal plane until a visual check shows the compound slide bar to be parallel to the reference surface of the sine bar. The parallel relationship between the two is then checked by mounting the gauge on the compound slide bar and moving the probe over the reference surface. If the gauge needle does not move, the two are deemed to be exactly parallel, and the position of the compound slide bar of the lathe is locked in place, being set up precisely to the desired tolerance; otherwise, the process is repeated. The sine bar is then removed from the lathe collet and replaced by the workpiece to be machined.
The compound sine bar of the present invention can be used in conjunction with cylindrical grinders and other spindle-type machines, as well as lathes, without the necessity of being mounted between centers. No device is available in the prior art for performing all of these functions. In addition, because of the rectangular shape of the base, the compound sine bar of the present invention can be supported on a flat surface to make measurements in the manner of prior art sine bars.